As raw materials for piezoelectric elements such as piezoelectric oscillators, piezoelectric ceramic compositions including Pb(Ti,Zr)O3 (lead titanate zirconate) or PbTiO3 (lead titanate) as a main component have been widely used. However, these are not preferable from the environmental point of view since these types of piezoelectric ceramic compositions contain a Pb component. Therefore, lead-free piezoelectric materials not containing a Pd component have been recently required.
Consequently, a piezoelectric ceramic composition including a main component having a composition represented by general formula (Ag1-xLix)(Nb1-yTay)O3, where 0.075≦x<0.40 and 0≦y<0.20, and an accessory component (not more than 5 parts by weight) containing at least one of a Mn oxide and a Si oxide has been already disclosed (Patent Document 1).
A piezoelectric element is generally required to have a high electromechanical coupling factor k33, which indicates the conversion efficiency when converting electrical energy applied between electrodes of a piezoelectric to mechanical energy. In Patent Document 1, a piezoelectric element having an electromechanical coupling factor k33 of 20% or more, which is the value needed to practical use, can be obtained by using a piezoelectric ceramic composition having the above-mentioned composition.
Further, Patent Document 2 discloses a ceramic material mainly used for a capacitor. The ceramic material contains two different types of components which are present in phases different from each other and each have a perovskite structure containing Ag in the A site and Nb and Ta in the B site. Specifically, the use of a composition (Ag1-yMIIIy)((Nb1-xTax)l-yMIVy)O3 (where MIII represents Bi or a rare-earth metal, MIV represents In, Sc or Ga, 0.35≦x≦0.5 and 0≦y≦0.1) or a composition (Ag1-yMIIIy)((Nb1-xTax)1-yMIVy)O3 (where MIII represents Ba, Ca, Pb, or Sr, MIV represents Sn or Zr, 0.35≦x≦0.5 and 0≦y≦0.1) is disclosed. In addition, it is disclosed that a microwave device having a high dielectric constant, i.e., ∈>300, a low dielectric loss and a small TK∈ can be obtained by using a composition disclosed in Patent Document 1.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-68836
Patent Document 2: PCT Japanese Translation Patent Publication No. 2004